In the Claus process, elemental sulfur is produced by reacting H.sub.2 S and SO.sub.2 in the presence of a catalyst. The Claus system uses a combustion chamber which, at 950.degree.-1,350.degree. C., converts 50 to 70% of sulfur contained in the feed gas into elemental sulfur. Sulfur is condensed by cooling the reaction gas to a temperature below the dew point of sulfur, after which the remaining gas is heated and further reacted over a catalyst. Normally, the gas passes through at least two such Claus catalyst stages.
The use of magnesium aluminate spinels for the oxidative sorption of SOx from effluent streams of the Claus process, followed by the reductive regeneration and reprocessing of the off-gas thus produced, has received recent attention as an attractive means to limit the potential for environmental damage which may be caused from the direct release of SOx.
The Mobil Oil SOx Treatment Process (MOST) is currently under development for a number of different applications. The first envisioned use of this technology, for Claus Tailgas scrubbing, was disclosed in U.S. Pat. No. 5,229,091. It consists of the oxidative sorption of SO.sub.2 onto a solid sorbent, preferably a magnesium aluminate spinel, followed by reductive regeneration to produce and effluent containing primarily SO.sub.2. with some H.sub.2 S and S. This effluent is then refed to the Claus Unit for further reaction. The sulfur oxide sorbed is ultimately transformed into elemental sulfur. Reductive desorbents (reducing gases) found to be successful for this are hydrogen, hydrocarbons (methane, propane), carbon monoxide/synthesis gas combinations, hydrogen sulfide, and ammonia.
In addition to the aforementioned Claus Tailgas scrubbing application, other modes of implementing this scheme have been put forth and investigated. Some of those modes involve the scrubbing of FCC tailgas in a manner similar to that described for Claus Tailgas operations. U.S. Pat. No. 5,547,648 discloses this concept. The MOST process has also been extended to gas field applications, process heat furnaces, and to coal or oil fired plants. The process for the oxidative sorption of SOx is similar in the applications listed here. The availability of reducing gases and related process equipment allows for a fairly wide number of applications for this technology.